This invention relates to cardiac pacemakers and in particular, to a new and improved electrode system for a pacemaker.
Cardiac pacemakers are widely used for stimulating the heart and controlling its rate. The heart has an internal electrical system. Electrical signals produced by the sino-atrial (SA) node control the heart beat under normal circumstances. These signals conduct from the SA node to the right atrium, and are transmitted through the heart to the right ventricle which responds to the transmitted signal producing contraction of the heart. Malfunction in the conduction system between atrium and ventricle sometimes results in failure of signal transmission. Cardiac pacemakers supply this missing signal to the ventricle and result in its beating at a fixed rate.
In a typical cardiac pacemaker, the electrical pulses are provided at a predetermined rate. In earlier versions, the electrode was sewn into the right ventricle requiring open heart surgery. Through later developments, the electrode was mounted in a catheter which was inserted through a vein permitting positioning of the electrode at the apex of the right ventricle, and thus eliminating the requirement for open heart surgery. With this type of pacemaker, the atrium is depolarized at physiologic body rate determined by signals from the SA node, while the ventricle operates at the predetermined rate controlled by the pacemaker. This is not a wholly satisfactory condition, particularly for active people who require a heart rate varying over a wide range, or for people with severely limiting heart disease.
In one approach to meeting this problem, two catheters were utilized, with one catheter positioned within the ventricle and one within the atrium. The stimulating electrodes of the two catheters are operated at a fixed rate but with a time lag between the stimulating pulses. This system, sometimes referred to as sequential pacing, is not widely used and can augment cardiac output by only 5-15%.
In a more recent system, the P-wave generated at the atrium is sensed by an electrode sewn into the atrium at the time of open heart surgery. The signal from the sensing electrode is connected to the pulse generator and controls the timing of the stimulating pulse applied to the electrode of the catheter positioned in the ventricle. This system provides for varying the heart rate as a function of body demand, but has not been satisfactory because of the open heart surgery required for implanting the sensing electrode in the atrium.
Other electrode configurations for cardiac catheters are shown in U.S. Pat. Nos. 3,825,015, 3,865,118, 3,903,897 and 4,154,247. In 3,825,105, two axially spaced ring electrodes are placed at the distal end and four more axially spaced ring electrodes are carried on the catheter spaced from the distal end so as to be located in the atrium. Both ventricle and atrium are stimulated and the two atrial electrodes providing best contact with the atrium are selected for use.
U.S. Pat. No. 3,865,118 discloses a system for sequential pacing. Two stimulating electrodes are provided in the atrium and two in the ventricle. Stimulating pulses are sent in sequence to the atrium and to the ventricle. An alternative form of synchronized pacing possibly useful on a short-term basis is discussed at column 7 lines 10-20. The patent states that the atrial electrode could act as a sensor of the patient's T waves, apparently as well as acting as a stimulating electrode, since the preceding sentence refers to atrial stimulating being an advantage. At column 8 lines 1-5, the patent indicates that more or less than two electrodes could be used, but no details of construction or use are given.
In U.S. Pat. No. 3,903,897, two axially spaced ring electrodes are placed at the distal end and two more axially spaced ring electrodes are carried on the catheter spaced from the distal end so as to be located in the atrium. Both pairs of electrodes are used for sensing, with the ventricle signal being used for a discrimination function. The ventricle electrodes are also used for stimulation. Although theoretically practical, extensive literature indicates that P waves thus sensed are generally of small amplitude and more significantly that discrimination of P waves from QRS complexes is virtually impossible. The performance of a ring electrode sensor is shown in FIG. 16, which will be described below.
U.S. Pat. No. 4,154,247 discloses a catheter having two stimulating electrodes for improved stimulation. In most disclosed embodiments one stimulating electrode is at the distal tip and the other is a ring spaced from the tip. The catheter is formed so that the ring makes direct contact with the tissue of the heart. In one embodiment, the catheter is branched with a stimulating ring electrode in each branch so that both electrodes can make contact.
It is an object of the present invention to provide a new and improved electrode system which will provide for varying the heart rate in response to the body demand while at the same time utilizing only a single catheter inserted through a vein, without calling for open heart surgery. A particular object of the invention is to provide a new and improved sensing electrode arrangement which produces one or more usable P-wave signals, or in one embodiment QRS signals, for stimulation and timing.
It is an object of the invention to provide a catheter for sensing and for stimulation in the form of a single nondiverging filament having a stimulating electrode at the distal tip and having two or more sensing electrodes closely adjacent each other and circumferentially mounted in the catheter equidistant from the tip.
It is another object to provide a new and improved signal handling circuit and process for generating and utilizing orthogonally related P type signals in achieving an improved P wave signal for use in a cardiac pacer, which signals may be manipulated in operational amplifiers and the like if desired.
It is a particular object of the invention to provide new and improved processes for controlling heart action using a sensed bipolar signal or orthogonal bipolar signals as inputs for controlling or inhibiting pace maker action. Another object is to provide new and improved electrode-heart configurations for stimulation of heart action. Other objects, advantages, features and results will more fully appear in the course of the following description.